The relations between the Roman Empire and the various tribes inhabiting territories next to its borders were the subject of active political actions, depending on the specific historical circumstances. The Marcomannic Wars of Marcus Aurelius were the result of yet another escalation of these relations. They are considered as one of the first serious manifestations of external pressure on the Empire from the free peoples living in the lands north and east of the Rhine-Danube frontier. The beginning of the prolonged military conflict was marked by the invasion of Germanic tribes into Pannonia. For several years, the main military operations were conducted primarily along the Upper and Middle Danube, extending eastward to Dacia. The territory of the Balkans, south of the Lower Danube, generally remained outside the scope of the main conflict, which led to parts of the military contingent from Lower Moesia being redirected toward Dacia – thus weakening the provincial defense of those regions. Taking advantage of the situation, in 170 AD the Costoboci crossed the Danube and devastated vast territories of Lower Moesia, Thrace, and Macedonia, reaching as far south as Attica. The event received only a feeble response in the surviving historical sources, which is one of the reasons for the sporadic scholarly interest in this episode of Balkan history.